W. Boschin

Optical Mass Estimates of Galaxy Clusters

We evaluate in a homogeneous way the optical masses of 170 nearby clusters (z ≤ 0.15). The sample includes both data from the literature and the new ESO Nearby Abell Clusters Survey (ENACS) data. On the assumption that mass follows the galaxy distribution, we compute the mass of each cluster by applying the virial theorem to the member galaxies. We constrain the masses of very substructured clusters (about 10% of our clusters) between two limiting values. After appropriate rescaling to the X-ray radii, we compare our optical mass estimates to those derived from X-ray analyses, which we compiled from the literature (for 66 clusters). We find a good overall agreement. This agreement is expected in the framework of two common assumptions: that mass follows the galaxy distribution and that clusters are not far from a situation of dynamical equilibrium, with both gas and galaxies reflecting the same underlying mass distribution. We stress that our study strongly supports the reliability of present cluster mass estimates derived from X-ray analyses and/or (appropriate) optical analyses.

Finding galaxy clusters using Voronoi tessellations

We present an objective and automated procedure for detecting clusters of galaxies in imaging galaxy surveys. Our Voronoi Galaxy Cluster Finder (VGCF) uses galaxy positions and magnitudes to find clusters and determine their main features: size, richness and contrast above the background. The VGCF uses the Voronoi tessellation to evaluate the local density and to identify clusters as significative density fluctuations above the background. The significance threshold needs to be set by the user, but experimenting with different choices is very easy since it does not require a whole new run of the algorithm. The VGCF is non-parametric and does not smooth the data. As a consequence, clusters are identified irrespective of their shape and their identification is only slightly affected by border effects and by holes in the galaxy distribution on the sky. The algorithm is fast, and automatically assigns members to structures. A test run of the VGCF on the PDCS field centered at

Characterizing K2 Planet Discoveries: A Super-Earth Transiting the Bright K Dwarf HIP 116454

\alpha = 13^{\rm h}26^{\rm m}

Rotation measures of radio sources in hot galaxy clusters

and δ = +

Cluster Abell 520: a perspective based on member galaxies A cluster forming at the crossing of three filaments?

29\degr

Internal dynamics of the radio halo cluster Abell 773: a multiwavelength analysis

52´(J2000) produces 37 clusters. Of these clusters, 12 are VGCF counterparts of the 13 PDCS clusters detected at the 3 σ level and with estimated redshifts from

K-Band Properties of Well-Sampled Groups of Galaxies

z=0.2

Internal dynamics of the massive cluster Abell 697: a multiwavelength analysis

to

Fossil group origins - II. Unveiling the formation of the brightest group galaxies through their scaling relations

z=0.6

Fossil groups origins I. RX J105453.3+552102 a very massive and relaxed system at z ∼0.5

. Of the remaining 25 systems, 2 are PDCS clusters with confidence level